D. D. Palmer founded chiropractic in the 1890s and his son B.J. Palmer helped to expand it in the early 20th century. It has two main groups: "straights", now the minority, emphasize vitalism, innate intelligence, spinal adjustments, and subluxation as the leading cause of all disease; "mixers" are more open to mainstream and alternative medical techniques such as exercise, massage, nutritional supplements, and acupuncture. Chiropractic is well established in the U.S., Canada and Australia.

For most of its existence, chiropractic has battled with mainstream medicine, sustained by ideas such as subluxation that are considered significant barriers to scientific progress within chiropractic. Vaccination remains controversial among chiropractors. In recent decades chiropractic has gained more legitimacy and greater acceptance among medical physicians and health plans and has had a strong political base and sustained demand for services, and evidence-based medicine has been used to review research studies and generate practice guidelines. Opinions differ as to the efficacy of chiropractic treatment and the efficacy and cost-effectiveness of maintenance chiropractic care are unknown. Although spinal manipulation can have serious complications in rare cases, chiropractic care is generally safe when employed skillfully and appropriately.

Chiropractic's early philosophy was rooted in vitalism, spiritual inspiration and rationalism. A philosophy based on deduction from irrefutable doctrine helped distinguish chiropractic from medicine, provided it with legal and political defenses against claims of practicing medicine without a license, and allowed chiropractors to establish themselves as an autonomous profession. This \"straight\" philosophy, taught to generations of chiropractors, rejects the inferential reasoning of the scientific method, and relies on deductions from vitalistic principles rather than on the materialism of science. However, most practitioners currently accept the importance of scientific research into chiropractic, and most practitioners are "mixers" who attempt to combine the materialistic reductionism of science with the metaphysics of their predecessors and with the holistic paradigm of wellness.

Although a wide diversity of ideas currently exists among chiropractors, they share the belief that the spine and health are related in a fundamental way, and that this relationship is mediated through the nervous system. Chiropractors study the biomechanics, structure and function of the spine, along with what they say are its effects on the musculoskeletal and nervous systems and its role in health and disease.

Chiropractic philosophy includes the following perspectives:

Holism assumes that health is affected by everything in people's complex environments; some sources also include a spiritual or existential dimension. In contrast, reductionism in chiropractic reduces causes and cures of health problems to a single factor, vertebral subluxation.

Conservativism considers the risks of clinical interventions when balancing them against their benefits. It emphasizes noninvasive treatment to minimize risk, and avoids surgery and medication.

Homeostasis emphasizes the body's inherent self-healing abilities. Chiropractic's early notion of innate intelligence can be thought of as a metaphor for homeostasis.

A patient-centered approach focuses on the patient rather than the disease, preventing unnecessary barriers in the doctor-patient encounter. The patient is considered to be indispensable in, and ultimately responsible for, the maintenance of health.

Schools of thought and practice styles

Range of belief perspectives in chiropractic

perspective attribute

potential belief endpoints

scope of practice:

narrow ("straight") ←

→ broad ("mixer")

diagnostic approach:

intuitive ←

→ analytical

philosophic orientation:

vitalistic ←

→ materialistic

scientific orientation:

descriptive ←

→ experimental

process orientation:

implicit ←

→ explicit

practice attitude:

doctor/model-centered ←

→ patient/situation-centered

professional integration:

separate and distinct ←

→ integrated into mainstream

taken from Mootz & Phillips 1997

Chiropractic is often described as two professions in one. Unlike the distinction between podiatry (a science-based profession for foot disorders) and foot reflexology (an unscientific philosophy which posits that many disorders arise from the feet), in chiropractic the two professions attempt to live under one roof. Significant differences exist amongst the practice styles, claims and beliefs between various chiropractors.

Straight chiropractors adhere to the philosophical principles set forth by D. D. and B. J. Palmer, and retain metaphysical definitions and vitalistic qualities. Straight chiropractors believe that vertebral subluxation leads to interference with an "Innate Intelligence" within the human nervous system and is a primary underlying risk factor for almost any disease. Straights view the medical diagnosis of patient complaints (which they consider to be the "secondary effects" of subluxations) to be unnecessary for treatment. Thus, straight chiropractors are concerned primarily with the detection and correction of vertebral subluxation via adjustment and do not "mix" other types of therapies. Their philosophy and explanations are metaphysical in nature and prefer to use traditional chiropractic lexicon (i.e. perform spinal analysis, detect subluxation, correct with adjustment, etc.). They prefer to remain separate and distinct from mainstream health care.

Mixer chiropractors "mix" diagnostic and treatment approaches from osteopathic, medical, and chiropractic viewpoints. Unlike straight chiropractors, mixers believe subluxation is one of many causes of disease, and they incorporate mainstream medical diagnostics and employ many treatments including conventional techniques of physical therapy such as exercise, massage, ice packs, and moist heat, along with nutritional supplements, acupuncture, homeopathy, herbal remedies, and biofeedback. Mixers tend to be open to mainstream medicine, and are the majority group.

Vertebral subluxation

Palmer hypothesized that vertebral joint misalignments, which he termed vertebral subluxations, interfered with the body's function and its inborn (innate) ability to heal itself. D.D. Palmer repudiated his earlier theory that vertebral subluxations caused pinched nerves in the intervertebral spaces in favor of subluxations causing altered nerve vibration, either too tense or too slack, affecting the tone (health) of the end organ. D.D. Palmer, using a vitalistic approach, imbued the term subluxation with a metaphysical and philosophical meaning. He qualified this by noting that knowledge of innate intelligence was not essential to the competent practice of chiropractic. This concept was later expanded upon by his son, B.J. Palmer and was instrumental in providing the legal basis of differentiating chiropractic medicine from conventional medicine. In 1910, D.D. Palmer theorized that the nervous system controlled health:

"Physiologists divide nerve-fibers, which form the nerves, into two classes, afferent and efferent. Impressions are made on the peripheral afferent fiber-endings; these create sensations that are transmitted to the center of the nervous system. Efferent nerve-fibers carry impulses out from the center to their endings. Most of these go to muscles and are therefore called motor impulses; some are secretory and enter glands; a portion are inhibitory their function being to restrain secretion. Thus, nerves carry impulses outward and sensations inward. The activity of these nerves, or rather their fibers, may become excited or allayed by impingement, the result being a modification of functionality—too much or not enough action—which is disease.

The concept of subluxation remains unsubstantiated and largely untested, and a debate about whether to keep it in the chiropractic paradigm has been ongoing for decades. In general, critics of traditional subluxation-based chiropractic (including chiropractors) are skeptical of its clinical value, dogmatic beliefs and metaphysical approach. While straight chiropractic still retains the traditional vitalistic construct espoused by the founders, evidence-based chiropractic suggests that a mechanistic view will allow chiropractic care to become integrated into the wider health care community. This is still a continuing source of debate within the chiropractic profession as well, with some schools of chiropractic (for example, Palmer College of Chiropractic) still teaching the traditional/straight subluxation-based chiropractic, while others (for example, Canadian Memorial Chiropractic College) have moved towards an evidence-based chiropractic that rejects metaphysical foundings and limits itself to primarily neuromusculoskeletal conditions. A 2003 survey of North American chiropractors found that 88% wanted to retain the term vertebral subluxation complex, and that when asked to estimate the percent of disorders of internal organs (such as the heart, the lungs, or the stomach) that subluxation significantly contributes to, the mean response was 62%. In 2005, subluxation was defined by the World Health Organization as "a lesion or dysfunction in a joint or motion segment in which alignment, movement integrity and/or physiological function are altered, although contact between joint surfaces remains intact. It is essentially a functional entity, which may influence biomechanical and neural integrity." This differs from the medical definition of subluxation as a significant structural displacement, which can be seen with static imaging techniques such as X-rays.

Scope of practice

Chiropractors, also known as doctors of chiropractic or chiropractic physicians in many jurisdictions, are primary-contact health care practitioners who emphasize the conservative management of the neuromusculoskeletal system without the use of medicines or surgery, with special emphasis on the spine. Chiropractic combines aspects from mainstream and alternative medicine: although chiropractors have many attributes of primary care providers, chiropractic has more of the attributes of a medical specialty like dentistry or podiatry. Mainstream health care and governmental organizations such as the World Health Organization consider chiropractic to be complementary and alternative medicine (CAM); however, a 2008 study reported that 31% of surveyed chiropractors categorized chiropractic as CAM, 27% as integrated medicine, and 12% as mainstream medicine.

The practice of chiropractic medicine involves a range of diagnostic methods including skeletal imaging, observational and tactile assessments, orthopedic and neurological evaluation, laboratory tests, and specialized tests. A chiropractor may also refer a patient to an appropriate specialist, or co-manage with another health care provider. Common patient management involves:

Chiropractors generally cannot write medical prescriptions; a 2003 survey of North American chiropractors found that a slight majority favored allowing them to write prescriptions for over-the-counter drugs. A notable exception is the state of Oregon which is considered to have an "expansive" scope of practice of chiropractic, which allows chiropractors to prescribe over-the-counter substances and perform minor surgery. In some locations chiropractors (DCs) and veterinarians (DVMs) with additional training and certification can practice veterinary chiropractic which includes the diagnosis, treatment and rehabilitation of injured animals. However, the official position of the American Chiropractic Association is that applying manipulative techniques to animals does not constitute chiropractic and that veterinary chiropractic is a misnomer.

Chiropractic medicine is established in the U.S., Canada, and Australia, and is present to a lesser extent in many other countries. Similar to other primary contact health providers, chiropractors can specialize in different areas of chiropractic medicine. The most common post-graduate diplomate programs include neurology, sports sciences, clinical sciences, rehabilitation sciences, orthopedics and radiology which generally require 2–3 additional years of additional post graduate study and passing competency examinations.

Treatment techniques

Spinal manipulation, which chiropractors call "spinal adjustment" or "chiropractic adjustment", is the most common treatment used in chiropractic care; in the U.S., chiropractors perform over 90% of all manipulative treatments. Spinal manipulation is a passive manual maneuver during which a three-joint complex is taken past the normal range of movement, but not so far as to dislocate or damage the joint; its defining factor is a dynamic thrust, which is a sudden force that causes an audible release and attempts to increase a joint's range of motion. More generally, spinal manipulative therapy (SMT) describes techniques where the hands are used to manipulate, massage, mobilize, adjust, stimulate, apply traction to, or otherwise influence the spine and related tissues; in chiropractic care SMT most commonly takes the form of spinal manipulation.

There are several schools of chiropractic adjustive techniques, although most chiropractors mix techniques from several schools. The following adjustive procedures were received by more than 20% of patients of licensed U.S. chiropractors in a 2003 survey: Diversified technique (full-spine manipulation), extremity adjusting, Activator technique (which uses a spring loaded tool to deliver precise adjustments to the spine), Thompson Technique, Gonstead (which looks at the whole spine with the philosophy that a vertebral misalignment may affect other areas of the spine, emphasizing the mechanical aspects of the spine), Cox/flexion-distraction (a gentle, non-force adjusting procedure which mixes chiropractic principles with osteopathic principles and utilizes specialized adjusting tables with movable parts), adjustive instrument, Sacro-Occipital Technique (which models the spine as a torsion bar), Nimmo Receptor-Tonus Technique, and Applied Kinesiology (which emphasises "muscle testing" as a diagnostic tool).

Education, licensing, and regulation

Chiropractors obtain a first professional degree in the field of chiropractic. The U.S. and Canada require a minimum 90 semester hours of undergraduate education as a prerequisite for chiropractic school, and at least 4200 instructional hours (or the equivalent) of full‐time chiropractic education for matriculation through an accredited chiropractic program. The World Health Organization (WHO) guidelines suggest three major full-time educational paths culminating in either a DC, DCM, BSc, or MSc degree. Besides the full-time paths, they also suggest a conversion program for people with other health care education and limited training programs for regions where no legislation governs chiropractic.

Upon graduation, there may be a requirement to pass national, state, or provincial board examinations before being licensed to practice in a particular jurisdiction. Depending on the location, continuing education may be required to renew these licenses.

In the U.S., chiropractic schools are accredited through the Council on Chiropractic Education (CCE) while the General Chiropractic Council (GCC) is the statutory governmental body responsible for the regulation of chiropractic in the UK. CCEs in the U.S., Canada, Australia and Europe have joined to form CCE-International (CCE-I) as a model of accreditation standards with the goal of having credentials portable internationally. Today, there are 18 accredited Doctor of Chiropractic programs in the U.S., 2 in Canada, 6 in Australasia, and 4 in Europe. All but one of the chiropractic colleges in the U.S. are privately funded, but in several other countries they are in government-sponsored universities and colleges. Chiropractic education in the U.S. is divided into straight or mixer educational curricula depending on the philosophy of the institution.

Regulatory colleges and chiropractic boards in the U.S., Canada, and Australia are responsible for protecting the public, standards of practice, disciplinary issues, quality assurance and maintenance of competency. There are an estimated 53,000 chiropractors in the U.S. (2006), 6526 in Canada (2006), 2500 in Australia (2000), and 1,500 in the UK (2000).

Abuse, fraud, and quackery are more prevalent in chiropractic than in other health care professions. A study of California disciplinary statistics during 1997–2000 reported 4.5 disciplinary actions per 1000 chiropractors per year, compared to 2.27 for MDs; the incident rate for fraud was 9 times greater among chiropractors (1.99 per 1000 chiropractors per year) than among MDs (0.20).

Utilization, satisfaction rates, and third party coverage

In the U.S., chiropractic is the largest alternative medical profession, and is the third largest doctored profession, behind medicine and dentistry. The percentage of population that utilizes chiropractic care at any given time generally falls into a range from 6% to 12% in the U.S. and Canada, with a global high of 20% in Alberta. The vast majority who seek chiropractic care do so for relief from back and neck pain and other neuromusculoskeletal complaints; most do so specifically for low back pain. Practitioners such as chiropractors are often used as a complementary form of care to primary medical intervention. Satisfaction rates are typically higher for chiropractic care compared to medical care, with a 1998 U.S. survey reporting 83% of persons satisfied or very satisfied with their care; quality of communication seems to be a consistent predictor of patient satisfaction with chiropractors. Public perception of chiropractic compares unfavorably with mainstream medicine with regard to ethics and honesty: in a 2006 Gallup Poll of U.S. adults, chiropractors rated last among seven health care professions for being very high or high in honesty and ethical standards, with 36% of poll respondents rating chiropractors very high or high; the corresponding ratings for other professions ranged from 62% for dentists to 84% for nurses.

Utilization of chiropractic care is sensitive to the costs incurred by the co-payment by the patient. The use of chiropractic declined from 9.9% of U.S. adults in 1997 to 7.4% in 2002; this was the largest relative decrease among CAM professions, which overall had a stable use rate. Employment of U.S. chiropractors is expected to increase 14% between 2006 and 2016, faster than the average for all occupations.

In the U.S., most insurances cover chiropractic. In Canada, there is lack of coverage under the universal public health insurance system. In Australia, most private health insurance funds cover chiropractic care, and the federal government funds chiropractic care when the patient is referred by a medical practitioner.

History

Chiropractic was founded in the 1890s by Daniel David (D.D.) Palmer in Davenport, Iowa. Palmer, a magnetic healer, hypothesized that manual manipulation of the spine could cure disease. Although initially keeping the theory a family secret, in 1898 he began teaching it to a few students at his new Palmer School of Chiropractic. One student, his son Bartlett Joshua (B.J.) Palmer, became committed to promoting chiropractic, took over the Palmer School in 1906, and rapidly expanded its enrollment. Prosecutions and incarcerations of chiropractors for practicing medicine without a license grew common, and to defend against medical statutes B.J. argued that chiropractic was separate and distinct from medicine, asserting that chiropractors "analyzed" rather than "diagnosed", and "adjusted" subluxations rather than "treated" disease. Early chiropractors believed that all disease was caused by interruptions in the flow of innate intelligence, a vital nervous energy or life force that represented God's presence in man; chiropractic leaders often invoked religious imagery and moral traditions. D.D. and B.J. both seriously considered declaring chiropractic a religion, which might have provided legal protection under the U.S. constitution, but decided against it partly to avoid confusion with Christian Science. Early chiropractors also tapped into the Populist movement, emphasizing craft, hard work, competition, and advertisement, aligning themselves with the common man against intellectuals and trusts, among which they included the American Medical Association (AMA).

Although D.D. and B.J. were "straight" and disdained the use of instruments, some early chiropractors, whom B.J. scornfully called "mixers", advocated use of instruments. In 1910 B.J. changed course and endorsed X-rays as necessary for diagnosis; this resulted in a significant exodus from the Palmer School of the more conservative faculty and students. The mixer camp grew until by 1924 B.J. estimated that only 3,000 of the U.S.'s 25,000 chiropractors remained straight. That year, B.J.'s promotion of the neurocalometer, a new temperature-sensing device, was another sign of chiropractic's gradual acceptance of medical technology, although it was highly controversial among B.J.'s fellow straights. Despite heavy opposition by organized medicine, by the 1930s chiropractic was the largest alternative healing profession in the U.S. The longstanding feud between chiropractors and medical doctors continued for decades. Until 1983, the AMA labeled chiropractic "an unscientific cult" and held that it was unethical for medical doctors to associate with an "unscientific practitioner". This culminated in a landmark 1987 decision, Wilk v. AMA, in which the court found that the AMA had engaged in unreasonable restraint of trade and conspiracy, and which ended the AMA's de facto boycott of chiropractic.

Serious research to test chiropractic theories did not begin until the 1970s, and was hampered by what are characterized as antiscientific and pseudoscientific ideas that sustained the profession in its long battle with organized medicine. By the mid 1990s there was a growing scholarly interest in chiropractic, which helped efforts to improve service quality and establish clinical guidelines that recommended manual therapies for acute low back pain. In recent decades chiropractic gained legitimacy and greater acceptance by medical physicians and health plans, and enjoyed a strong political base and sustained demand for services. However, its future seemed uncertain: as the number of practitioners grew, evidence-based medicine insisted on treatments with demonstrated value, managed care restricted payment, and competition grew from massage therapists and other health professions. The profession responded by marketing natural products and devices more aggressively, and by reaching deeper into alternative medicine and primary care.

Evidence basis

The principles of evidence-based medicine have been used to review research studies and generate practice guidelines outlining professional standards that specify which chiropractic treatments are legitimate and perhaps reimbursable under managed care. Evidence-based guidelines are supported by one end of an ideological continuum among chiropractors; the other end employs what is considered by many chiropractic researchers to be antiscientific reasoning and unsubstantiated claims, that have been called ethically suspect when they let practitioners maintain their beliefs to patients' detriment. A 2007 survey of Alberta chiropractors found that they do not consistently apply research in practice, which may have resulted from a lack of research education and skills. Evidence-based chiropractors possess the ability to apply research in practice. Continued education enhances the scientific knowledge of the practitioner.

Effectiveness

There is a wide range of ways to measure treatment outcomes. Opinions differ as to the efficacy of chiropractic treatment; many other medical procedures also lack rigorous proof of effectiveness. Chiropractic care, like all medical treatment, benefits from the placebo response. The efficacy of maintenance care in chiropractic is unknown.

Most research has focused on spinal manipulation (SM) in general, rather than solely on chiropractic SM. Some of this research has been criticized as being misleading for failing to mention incorporation of data derived from studies of SM that do not relate to chiropractic SM; defenders have replied that SM research is equally of value regardless of practitioner. There is little consensus as to who should administer the SM, raising concerns by chiropractors that orthodox medical physicians could "steal" SM procedures from chiropractors; the focus on SM has also raised concerns that the resulting practice guidelines could limit the scope of chiropractic practice to treating backs and necks. Many controlled clinical studies of SM are available, but their results disagree, and they are typically of low quality. It is hard to construct a trustworthy placebo for clinical trials of spinal manipulative therapy (SMT), as experts often disagree about whether a proposed placebo actually has no effect. Although a 2008 critical review found that with the possible exception of back pain, chiropractic SM has not been shown to be effective for any medical condition, and suggested that many guidelines recommend chiropractic care for low back pain because no therapy has been shown to make a real difference, a 2008 supportive review found serious flaws in the critical approach, and found that SM and mobilization are at least as effective for chronic low back pain as other efficacious and commonly used treatments.

Available evidence covers the following conditions:

Low back pain. There is continuing conflict of opinion on the efficacy of SMT for nonspecific (i.e., unknown cause) low back pain; methods for formulating treatment guidelines differ significantly between countries, casting some doubt on the guidelines' reliability. A 2007 U.S. guideline weakly recommended SM as one alternative therapy for spinal low back pain in nonpregnant adults when ordinary treatments fail, whereas the Swedish guideline for low back pain was updated in 2002 to no longer suggest considering SMT for acute low back pain for patients needing additional help, possibly because the guideline's recommendations were based on a high evidence level. A 2008 review found strong evidence that SM is similar in effect to medical care with exercise, and moderate evidence that SM is similar to physical therapy and other forms of conventional care. A 2007 literature synthesis found good evidence supporting SM and mobilization for low back pain and exercise for chronic low back pain; it also found fair evidence supporting customizable exercise programs for subacute low back pain, and supporting assurance and advice to stay active for subacute and chronic low back pain. Of four systematic reviews published between 2000 and May 2005, only one recommended SM, and a 2004 Cochrane review stated that SM or mobilization is no more or less effective than other standard interventions for back pain. A 2005 systematic review found that exercise appears to be slightly effective for chronic low back pain, and that it is no more effective than no treatment or other conservative treatments for acute low back pain.

Whiplash and other neck pain. There is no overall consensus on manual therapies for neck pain. A 2008 review found evidence that educational videos, mobilization, and exercises appear more beneficial for whiplash than alternatives; that SM, mobilization, supervised exercise, low-level laser therapy and perhaps acupuncture are more effective for non-whiplash neck pain than alternatives but none of these treatments is clearly superior; and that there is no evidence that any intervention improves prognosis. A 2007 review found that SM and mobilization are effective for neck pain. Of three systematic reviews of SM published between 2000 and May 2005, one reached a positive conclusion, and a 2004 Cochrane review found that SM and mobilization are beneficial only when combined with exercise, the benefits being pain relief, functional improvement, and global perceived effect for subacute/chronic mechanical neck disorder. A 2005 review found consistent evidence supporting mobilization for acute whiplash, and limited evidence supporting SM for whiplash.

Headache. A 2006 review found no rigorous evidence supporting SM or other manual therapies for tension headache. A 2005 review found that the evidence was weak for effectiveness of chiropractic manipulation for tension headache, and that it was probably more effective for tension headache than for migraine. A 2004 review found that SM may be effective for migraine and tension headache, and SM and neck exercises may be effective for cervicogenic headache. Two other systematic reviews published between 2000 and May 2005 did not find conclusive evidence in favor of SM.

Other. There is a small amount of research into the efficacy of chiropractic treatment for upper limbs, and a lack of higher-quality publications supporting chiropractic management of leg conditions. A 2007 literature synthesis found fair evidence supporting assurance and advice to stay active for sciatica and radicular pain in the leg. There is very weak evidence for chiropractic care for adult scoliosis (curved or rotated spine) and no scientific data for idiopathic adolescent scoliosis. A 2007 systematic review found that few studies of chiropractic care for nonmusculoskeletal conditions are available, and they are typically not of high quality; it also found that the entire clinical encounter of chiropractic care (as opposed to just SM) provides benefit to patients with asthma, cervicogenic dizziness, and baby colic, and that the evidence from reviews is negative, or too weak to draw conclusions, for a wide variety of other nonmusculoskeletal conditions, including ADHD/learning disabilities, dizzinesss, and vision conditions. Other reviews have found no evidence of benefit for asthma, baby colic, bedwetting, carpal tunnel syndrome, fibromyalgia, menstrual cramps, or pelvic and back pain during pregnancy.

Safety

Chiropractic care in general is safe when employed skillfully and appropriately. Manipulation is regarded as relatively safe, but as with all therapeutic interventions, complications can arise, and it has known adverse effects, risks and contraindications. Absolute contraindications to spinal manipulative therapy are conditions that should not be manipulated; these contraindications include rheumatoid arthritis and conditions known to result in unstable joints. Relative contraindications are conditions where increased risk is acceptable in some situations and where low-force and soft-tissue techniques are treatments of choice; these contraindications include osteoporosis. Although most contraindications apply only to manipulation of the affected region, some neurological signs indicate referral to emergency medical services; these include sudden and severe headache or neck pain unlike that previously experienced.

Spinal manipulation is associated with frequent, mild and temporary adverse effects, including new or worsening pain or stiffness in the affected region. They have been estimated to occur in 34% to 55% of patients, with 80% of them disappearing within 24 hours. Rarely, spinal manipulation, particularly on the upper spine, can also result in complications that can lead to permanent disability or death; these can occur in adults and children. The incidence of these complications is unknown, due to high levels of underreporting and to the difficulty of linking manipulation to adverse effects such as stroke, which is a particular concern. Several case reports show temporal associations between interventions and potentially serious complications. Vertebrobasilar artery stroke is statistically associated with chiropractic services in persons under 45 years of age, but it is similarly associated with general practitioner services, suggesting that these associations are likely explained by preexisting conditions. Weak to moderately strong evidence supports causation (as opposed to statistical association) between cervical manipulative therapy (whether chiropractic or not) and vertebrobasilar artery stroke.

Cost-effectiveness

A 2006 qualitative review found that the research literature suggests that chiropractic obtains at least comparable outcomes to alternatives with potential cost savings. A 2006 UK systematic cost-effectiveness review found that the reported cost-effectiveness of chiropractic manipulation compares favorably with other treatments for back pain, but that reports are based on data from clinical trials without sham controls and that the specific cost-effectiveness of the treatment (as opposed to non-specific effects) remains uncertain. A 2005 systematic review of economic evaluations of conservative treatments for low back pain found that significant quality problems in available studies meant that definite conclusions could not be drawn about the most cost-effective intervention. The cost-effectiveness of maintenance chiropractic care is unknown.

Vaccination

Within the chiropractic community there are significant disagreements about vaccination, one of the most cost-effective forms of prevention against infectious disease. Most chiropractic writings on vaccination focus on its negative aspects, claiming that it is hazardous, ineffective, and unnecessary. Some chiropractors have embraced vaccination, but a significant portion of the profession rejects it, as original chiropractic philosophy traces diseases to causes in the spine and states that vaccines interfere with healing. The American Chiropractic Association and the International Chiropractors Association support individual exemptions to compulsory vaccination laws, and a 1995 survey of U.S. chiropractors found that about a third believed there was no scientific proof that immunization prevents disease. The Canadian Chiropractic Association supports vaccination; a survey in Alberta in 2002 found that 25% of chiropractors advised patients for, and 27% against, vaccinating themselves or their children. A survey of Canadian Memorial Chiropractic College students in 1999–2000 reported that seniors opposed vaccination more strongly than freshmen, with 29.4% of fourth-year students opposing vaccination.